Pressure-sensitive recording material

ABSTRACT

This invention provides a pressure-sensitive recording material in which two color-forming components capable of forming a colored substance upon reaction with each other are formed on the surfaces of separate supports, for example paper sheets, as a transferable coated layer and a receptive coated layer respectively, said transferable coated layer being a layer of a hot-melt type coating containing one color-forming component, and said receptive coated layer being a layer having absorbent micropores and composed of microcapsules containing the other color-forming component, a fine powder and a binder. By stacking a plurality of such pressure-sensitive recording materials, they can be used as a pressure-sensitive recording business form.

FIELD OF TECHNOLOGY

This invention relates to a pressure-sensitive recording material whichcan produce multiple copies when pressure such as printing or writingpressure, is exerted thereon. More specifically, it relates to apressure-sensitive recording material having a surface coated layer of anovel structure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 to 3 are examples of prior art pressure-sensitive recordingmaterials in which two color-forming components are coated on thesurfaces of supports in a face-to-face relationship;

FIGS. 4 and 5 show examples of coated layers in the present invention;and

FIG. 6 shows an example of a spot-type pressure-sensitive recordingbusiness form which utilizes the pressure-sensitive recording materialsof this invention. All of these drawings are cross-sectional views.

In the drawings, 1 represents a support; 2, a microcapsular layercontaining a liquid comprising a color-forming agent; 3, a layer of asolid containing a coloring agent; 4 and 5, layers formed byspot-coating only the desired portions with a hot-melt type coatingcontaining a color-forming agent; 5', a layer formed by coating theentire surface with the hot-melt type coating; and 6, a layer havingabsorbent micropores consisting of microcapsules, a fine powder and abinder.

BACKGROUND TECHNOLOGY

Pressure-sensitive recording materials having two color-formingcomponents coated on the surfaces of separate supports, which haveconventionally gained widespread use, are of the type shown in FIG. 1.Specifically, one of the color-forming components is encapsulated inmicrocapsules (2) and coated on the undersurface of an upper support(1), and the other color-forming component is present as a coated layer(3) on the top surface of a lower support (1). When a printing orwriting pressure is applied to such a pressure-sensitive material, theliquid contained in the microcapsules (2) flows out and is transferredto, and absorbed by, the coated layer (3), and simultaneously, the twocolor-forming components react with each other to form a coloredsubstance and thus to form an image on the receptive surface of thecoated layer (3).

When, in the material of the type shown in FIG. 1, the upper support andthe lower support are superimposed and cut or bent, colored stains occurat the parts to which pressure is applied. There is known apressure-sensitive recording sheet in which microcapsules (2) containinga color-forming component are spot-coated on the undersurface of theupper support, as shown in FIG. 2, in order to inhibit or avoid theoccurrence of such an inconvenience. In practice, however, thestop-coating of microcapsules is difficult, because tough capsules whichwithstand spot-coating are difficult to obtain, and creases form on thecoated support because of the use of a water-base coating, etc.

It was thus proposed to form a transferable spot-coated layer (4) byspot-coating a so-called hot-melt ink resulting from the dispersion of acolor-forming component in a hot-melt type wax on the undersurface ofthe upper support (1), as shown in FIG. 3. Although in this type, thecolor-forming components contained in the transferable coated layer (4)and the receptive coated layer (3) are enveloped by another component(e.g., wax, binder, etc.), when the upper support and the lower supportare handled in the superimposed state, colored stains occur under anunexpected exterior force. Furthermore, when a printing or writingpressure is applied, the transferable coated layer (4) is transferred tothe receptive coated layer (3), and conversely, the receptive layer (3)is transferred to the transferable layer (4). This results in theformation of an image on both coated layers, and the rate of colorformation and the density of the color formed in the receptive coatedlayer are frequently reduced. If, in an attempt to remove such aninconvenience, the formulation is changed so that the transferablecoated layer (4) may not easily be transferred, color formation upon theapplication of a printing or writing pressure is poor so that a clearimage cannot be obtained.

DISCLOSURE OF THE INVENTION

As a material which removes these inconveniences, the present inventionprovides a pressure-sensitive recording material comprising atransferable coated layer of a hot-melt type coating containing onecolor-forming component and a receptive coated layer having absorbentmicropores and consisting of microcapsules which contain anothercolor-forming component, a fine powder and a binder. FIGS. 4 and 5illustrate this invention. FIG. 4 shows a material in which atransferable coated layer (5) is spot-coated on the undersurface of anupper support (1), and FIG. 5 shows a material in which a transferablecoated layer (5) is coated on the entire undersurface of the uppersupport (1). In these figures, (6) represents a layer having absorbentmicropores and consisting of the microcapsules, a fine powder and abinder, which is applied to the top surface of the lower support (1).

As stated above, many pressure-sensitive recording sheets are of thetype in which microcapsules containing one color-forming component as aliquid are kept present in the transferable coated layer when the liquidin the capsules is caused to be transferred to the opposite receptivesurface to form a color thereon. In this case, not all of the liquid inthe capsules is transferred to the receptive surface, and some remainson the transfer surface without contributing to color formation. Incontrast, the present invention is based on the theory thatmicrocapsules are caused to be present in the receptive layer and theliquid therein flows out and is absorbed in the layer, instead ofcausing microcapsules containing a color-forming component to be presentin the transferable coated layer and transferring them to the receptivecoated layer. Because the color-forming component in the capsuleschanges effectively to a colored substance which directly forms an imageon the receptive surface, both the rate of color formation and thedensity of the color formed increase. For the same reason, it is notnecessary to incorporate a large amount of the coloring component. Thus,the first feature of the present invention is that microcapsulescontaining one color-forming component are included in the receptivecoated layer.

The second feature of the present invention is the use of a hot-melttype coating containing a color-forming component in the transferablecoated layer. As is well known, the hot-melt type coating is called ahot-melt ink or hot-melt wax, and has the advantage that this coating iseasy to spot-coat and needs only to be cooled after coating without theneed for drying, and moreover, the coating head is simple and the rateof coating can be increased. When the hot-melt coating is used in theconstruction shown in FIG. 3, inconveniences are caused. However, whenin accordance with this invention, the transferable coated layercomposed of such a hot-melt coating containing a color-forming componentis combined with the structure in which the microcapsules are includedin the receptive coated layer, i.e. the first feature described above,the advantages of the two cooperate with each other to give goodresults.

The combination of the first and second features alone is stillinconvenient, however. If the microcapsules are ruptured immediatelybefore the hot-melt type coating of the transferable coated layer istransferred upon the application of printing pressure to the surfaces ofthe microcapsules in the receptive coated layer, the liquid comes outand is transferred to the transferable coated layer to form a color. Orbecause the hot-melt type coating cannot be transferred, an image is notformed well. Hence, the results are undesirable.

Thus, according to this invention, the receptive coated layer is formedas a layer of the structure having absorbent micropores and composed ofmicrocapsules, a fine powder and a binder, and the liquid which comesout upon the application of pressure is instantaneously and completelyabsorbed in the receptive coated layer. By so doing, the hot-melt typecoating is completely transferred, and back-transferring of the liquiddoes not occur. The layer of the structure having absorbent microporesalso has an action of protecting the microcapsules against an externalforce.

In preparing the receptive coated layer, appropriate conditionscorresponding to the size of the capsules, the amount of the binder, andthe shape, size and size distribution of the fine powder should beselected so that the volume of the pores is larger than the total volumeof the liquid in the capsules to provide absorbent micropores having theaforesaid function. The following table shows experimental exampleswhich show the relation of the blending proportions of the capsules, thefine powder and the binder in the preparation of a receptive layer tothe function of the receptive layer formed. In these experiments, ahot-melt coating containing 30% of Silton Clay (a product of MizusawaKagaku) was used as the transferable layer.

    __________________________________________________________________________    Examples of formulation of the receptive coated layer                         and the densities of colors                                                   Run No.            1   2   3   4   5   6   7  8                               __________________________________________________________________________    Amounts                                                                             Microcapsules (1)                                                                          50  40  30  25  20  15  10  5                              blended                                                                             Precipitated calcium                                                    (parts)                                                                             carbonate (2)                                                                              45  45  45  45  45  45  45 45                                    Polyvinyl alcohol (3)                                                                      15  15  15  15  15  15  15 15                              Microcapsules in the coated layer (%)                                                            45.5                                                                              40.0                                                                              33.3                                                                              29.4                                                                              25.0                                                                              20.0                                                                              14.3                                                                              7.7                            Density                                                                             Receptive coated surface                                                                   +++ +++ +++ +++ +++ +++ ++ ++                              of image                                                                            Transferable coated                                                           surface      +++ +++ +++ ++  ++  -   -  -                               __________________________________________________________________________     +++: High density;                                                            ++: medium density;                                                           +: low density;                                                               -: density nearly zero.                                                       (1) Gelatin capsules obtained in a customary manner (containing a             colorless dye).                                                               (2) A product of Shiraishi Calcium (PC), average particle size 2 microns.     (3) A product of Denki Kagaku (Denka Size A50).                          

The formation and effect of absorbent micropores are described further.

Generally, in order for a liquid to penetrate into a capillary and reacha distant point, the diameter of the capillary should be as small aspossible. However, in order for a large amount of the liquid to beabsorbed within short periods of time, the diameter of the capillaryshould be as large as possible. In the receptive coated layer in thisinvention, it is desirable for the liquid which has flowed from themicrocapsules to be instantaneously and completely absorbed by theaforesaid coated layer. Consequently it is desirable that the diameterof absorbent micropores should be large. However, since the size of themicrocapsules is usually about 1 to 10 microns and the amount of theliquid contained in the microcapsules is small, if the diameter of poresexisting in the neighborhood is too large, the liquid does not at allmove along the pores, that is, it is not absorbed. Accordingly, thediameter of the absorbent micropores should be smaller than about 10microns. Furthermore, in order to increase the ability of absorbingliquid, the total volume of the pores should be large.

Usually, the microcapsules are spherical when they are dispersed in aliquid, but when they are coated and dried, they form a nearlycontinuous phase with not so much interstices left among themicrocapsules. Thus, the interstices are filled with the powder or afine fibrous powder in order to leave fine spaces after drying.

Generally speaking, when spheres of the same diameter are filled in abox, 26% of the space remains in the case of closest packing, and 50% ofthe space remains in the case of bulky packing. In a cylindricalfilament, 22% of the space likewise remains. Thus, if a coated layer isformed on a support by means of a coating composed of microcapsules andvarious fine powders and dried, the aforesaid space should remain.However, if a binder is added to prevent picking of the dried coatedlayer, the amount of the space decreases according to the amount of thebinder in the layer. If the amount of the binder increases beyond theamount of the space, no absorbent micropore will remain.

The above is based on presumption from calculated values. The finepowders in actual use are not spherical or cylindrical but irregularlyshaped. Thus, the particle size distribution exists continuously, andthere may be a deviation from the calculated values. The above tableshows a part of this situation. When the receptive layer and thetransferable layer are set opposite to each other and letters areprinted, an image appears in the transferable layer upon the migrationof the color-forming component in the microcapsules to the color-formingcomponent of the transferable layer. This shows that the liquidcontained in the ruptured microcapsules cannot be fully absorbed by thereceptive layer and the excess of the liquid is transferred to thetransferable surface. In the above experiments, when the amount of themicrocapsules in the receptive coated layer is less than 20%, the liquidin the microcapsules is all absorbed by the receptive coated layer toprevent coloration at the transferable coated layer.

The total volume of the absorbent micropores which gives such an effecthas to do not only with the amount of a fine powder to be blended, butalso directly with the amount of the binder added. The total pore volumedecreases when the binder is added in a large amount, and increases whenit is added in a small amount. Moreover, when the support is absorbent,it absorbs the binder incorporated in the coating, and changes theamount of the binder remaining in the dried coated layer. Accordingly,the absorbency of the support also affects the total pore volume.

In the examples of coating formulations shown in the above table,wood-free paper having a basis weight of 43 g/m² is used as a support,and precipitated calcium carbonate and polyvinyl alcohol are added tomicrocapsules. Depending upon the materials used, for example upon theselection of the support, microcapsules, fine powder or binder, the sameresults are not always obtained. Usually, good results can be obtainedby adjusting the proportions of the individual components in the coatedlayer as follows:

    ______________________________________                                        Microcapsules:       10 to 35%                                                Fine powder:         70 to 50%                                                Binder:              20 to 15%                                                ______________________________________                                    

Of course, the proportions of the fine powder and the binders should beselected properly within the aforesaid ranges in order to form absorbentmicropores of the desired volume. In short, in the present invention,the amounts of the fine powder and binder should be selected properly sothat the total amount of the liquid in the microcapsules does not exceedthe total pore volume of the absorbent micropores formed in thereceptive coated layer.

The support in this invention is mainly paper. However, since in thisinvention the receptive coated layer is given the ability to absorb aliquid, a non-absorbent material such as plastic films and metal foilsmay optionally be used. Thus, there is no particular limit to thematerial for the support.

As the color-forming components, various combinations of compounds whichreact with each other to form a colored substance can be used. Since inthis invention, one component of the combination is used in the form ofa hot-melt type coating, substances having strong volatility at about100° C. or substances which are liquid at room temperature areundesirable. There can be used combinations of colorless dyes of thetriphenylmethane phthalide, fluoran, phenothiazine, indolyl phthalide,leuco auramine, spiropyran, triphenylmethane, triazene, naphtholactam,benzopyrane, azomethine, hydroxyphthalane types, etc. with inorganiccolor developing agents such as activated clay, colloidal silica orzeolite and various organic color developing agents. The compounds inthese combinations may be used interchangeably in the transferablecoated layer and the receptive coated layer. A combination of a ferricsalt of a fatty acid with a higher alcohol ester of gallic acid, and acombination of a vanadium compound such as stearyl trimethyl ammoniumvanadate and a higher alcohol ester of gallic acid are also used. Ifdesired, these combinations may be used as mixtures.

The fine powder, as used in the present invention, denotes variousinorganic and organic white pigments, starch particles, wood cellulosepowder, etc. It should not be one which forms a color upon contact withthe microcapsules containing a color-forming component. This is becauseeven when the color-forming component is kept inside the microcapsules,it is by no means sure that the color-forming component does not at alladhere to the outside wall of the capsules. For example, for capsulescontaining crystal violet lactone, etc., fine powders which do not causecolor formation, such as calcium carbonate or aluminum hydroxide aredesirable.

In addition, the shape, size and size distribution of the fine powderhave to do with the formation of absorbent micropores, and becomefactors which determine the rate and amount of absorbing the liquid inthe capsules. Although it is difficult to express these parameters bynumerical figures, desirable fine powders are those which exhibit anearly spherical shape and have a particle diameter of 0.5 to 20 micronsand a particle size distribution which is concentrated as much aspossible on one point. The wood cellulose powder desirably has a size ofless than 300 mesh.

Natural and synthetic polymers which do not form a color with thecolor-forming component are used as the binder. Since the amount of thebinder added is an important factor in forming absorbent micropores, itshould be determined so as to maintain a balance against the amount ofthe capsules by considering the aforesaid calculated values of theremaining space at the time of filling spherical bodies into a box andthe shape, size and size distribution of the fine powder used.

Since the hot-melt type coating should be transferable, it is desirableto form a primer layer before its coating. As the primer, theabove-exemplified polymers used as binders may be used. Those havinggood effect of sealing are selected.

Materials for the hot-melt type coating other than the color-formingcomponent include, for example, high-melting natural waxes such ascarnauba wax, candelilla wax and montan wax, oils and fats, hardenedoils, higher fatty acids, polyvalent metal salts of higher fatty acids,petroleum waxes, and other involatile high-melting substances. Ifdesired, minor amounts of involatile solvents may be added. Furthermore,stabilizers such as antioxidants and ultraviolet absorbents may be addedas required.

POSSIBILITY OF UTILIZATION IN INDUSTRY

A stack of a plurality of the pressure-sensitive recording materials ofthis invention can be used as a pressure sensitive recording businessform.

BEST MODE OF PRACTICING THE INVENTION

The present invention is illustrated specifically by the followingExamples. These Examples are for the purpose of illustrating preferredmodes of practicing the invention, and the invention is not limitedthereto.

EXAMPLE 1

Microcapsules containing colorless dyes were prepared in the followingmanner.

Crystal violet lactone (50 g) and 30 g of benzoyl leuco methylene bluewere dissolved in alkylnaphthalene (KMC-113, Kureha Chemical) to form1000 g of a solution. The solution was dispersed in a solution of 200 gof gelatin in 1500 g of water with stirring at high speed by ahomomixer. Then, a solution of 40 g of carboxy methyl cellulose in 3000g of water was added. Furthermore, 2000 g of water was added. Then, 90 gof 10% acetic acid was added to adjust the pH of the mixture to 4.0. Thesolution was then cooled with ice to 7° C., and 150 g of 37%formaldehyde was added, and then 300 g of 4% sodium hydroxide was addedto adjust the pH of the mixture to 9.0. The mixture was maintained at50° C. for 1 hour, and 200 g of wood cellulose powder (KC Flock-300,Sanyo Kokusaku Pulp) was added. The mixture was then stored at roomtemperature. If desired, some amount of an ultraviolet absorbent may beadded to the alkylnaphthalene.

The formulation (parts by weight) of a coating for the receptive coatedlayer was as follows:

    ______________________________________                                        Aforesaid microcapsular solution (solids)                                                                 15                                                Precipitated calcium carbonate                                                (Shiraishi Calcium)         45                                                Polyvinyl alcohol (Denki Kagaku)                                                                          15                                                ______________________________________                                    

An aqueous dispersion of the above formulation having a solidsconcentration of 18% was coated by an air knife at a rate of 3.5 g/m² onwood free paper having basis weight of 40 g/m² and consisting of 70%LBKP and 30% NBKP. An 8% polyvinyl alcohol solution had been coated onthe back surface of the paper by a Meyer bar to prevent curling and givebarrier property as a primer for the transferable coated layer. Then, ahot-melt type coating for the transferable coated layer consisting ofthe following formulation was spot-coated at a rate of 3.0 g/m² by ahot-melt transfer gravure technique to that surface of the paper whichhad been given barrier property as above. The formulation (parts byweight) of the hot-melt coating was as follows:

    ______________________________________                                        Silton Clay (Mizusawa Kagaku)                                                                           300                                                 Stearic acid              300                                                 Hardened castor oil       100                                                 Carnauba wax              100                                                 Beef tallow               200                                                 ______________________________________                                    

The above ingredients were melt-mixed by a kneader at 80° C., and usedas the hot-melt type coating.

Ten paper sheets coated both at the top and back surfaces in the abovemanner were superimposed to form a pressure-sensitive recording businessform of the structure shown in FIG. 6 (the illustration of sixintermediate sheets is omitted). When letters were printed on theresulting assembly by an electric typewriter, clear blue letters couldbe rapidly printed even on the lowermost sheet (10th sheet).

When relief printing was performed on the surface of the receptivecoated layer, troubles were not seen as was the case with reliefprinting on wood free paper.

When a pressure-sensitive recording business form as made in the sameway as above using the receptive coated layer obtained in Run No. 7 inthe above table, the same good results as above were obtained.

EXAMPLE 2

In the same way as in Example 1, microcapsules containing an ironcompound were prepared. That is, 80 g of a ferric salt of mixed coconutoil fatty acid was dissolved in oxyethylene lauryl ether (Actinol,Matsumoto Kosan) to form 1000 g of a solution. Using the resultingsolution, microcapsules were prepared.

A coating for a receptive coated layer was also prepared in accordancewith Example 1.

The formulation (parts by weight) of a hot-melt type coating for atransferable coated layer opposite thereto was as follows:

    ______________________________________                                        Lauryl gallate              80                                                Stearic acid               300                                                Hardened castor oil        120                                                Glycerol monostearate      100                                                Carnauba wax               100                                                Beef tallow                200                                                Aluminum hydroxide (Shoden H-42)                                                                         100                                                ______________________________________                                    

Ten coated sheets obtained in accordance with Example 1 weresuperimposed and letters were printed on the assembly. The rate of colorformation was somewhat lower than in Example 1, but a black image havinggood fastness to light was obtained.

We claim:
 1. A pressure-sensitive recording material in which twocolor-forming components capable of forming a colored substance uponreaction with each other are formed on the surfaces of separate supportsas a completely transferable coated layer and a receptive coated layerrespectively, said transferable coated layer being a layer of a hot-melttype coating containing one color-forming component, and said receptivecoated layer being a layer having absorbent micropores and composed of10 to 35% of microcapsules containing a liquid containing the othercolor-forming component, 70 to 50% of a fine powder which does not reactwith the color-forming components to form a color, and 20 to 15% of abinder which does not react with the color-forming components to form acolor, the diameter of said micropores being less than 10 microns, andthe total volume of the micropores being greater than the total volumeof the liquid within the microcapsules.
 2. The pressure-sensitiverecording material set forth in claim 1 wherein the fine powder has aparticle diameter of 0.5 to 20 microns.
 3. The pressure-sensitiverecording material set forth in claim 1 or 2 wherein said supports arepaper sheets, plastic films or metal foils.
 4. The pressure-sensitiverecording material set forth in claim 1 or 2 wherein said layer ofhot-melt type coating consists of one of the color-forming componentsand a high-melting natural wax, an oil, a fat, a higher fatty acid, apolyvalent metal salt of a higher fatty acid, a petroleum wax or anotherinvolatile high-melting substance.
 5. The pressure-sensitive recordingmaterial set forth in claim 1 or 2 wherein said fine powder is aninorganic white pigment, an organic white pigment, starch particles, orwood cellulose powder.
 6. The pressure-sensitive recording material setforth in claim 1 or 2 wherein said binder is a natural or syntheticpolymer.